This invention pertains to the art of die presses and more particular to a coining press.
The invention is particularly applicable to an assembly for selectively coining a corner break or chamfer on an oil metering flat of a rotary valve rotor useful in a power steering assembly. However, it will be appreciated to those skilled in the art that the invention could be readily adapted for use in other environments as, for example, where similar precision coining assemblies and methods are employed for the manufacture of various other types of items.
Power steering rotary valve constructions are well known in the art as well as the advantages of providing precision corner breaks on rotor oil metering flats. (See U.S. Pat. No. 4,103,407 to Elizalde, et al.) The advantage of such a corner break is to provide a smoother operating power steering assembly. For example, with reference to FIG. 4, an illustrative graph is shown demonstrating that a rotor valve including a coined corner break at the oil metering flat requires a greater time for the power steering cylinder to reach its full volume. Operation of a rotor valve to reach full fluid volume without a coined metering flat requires substantially less time than one with a coined metering flat. By extending the time to get full action of the power steering mechanisms, the overall power steering assembly is smoothed and problems of oversteering, excessive responsiveness, and sensitivity are avoided.
Various forms and types of assemblies and methods for coining a metering flat corner break have heretofore been suggested and employed in the industry, all with varying degrees of success. It has been found that the defects present in most prior assemblies and methods are such that they are of limited economic and practical value. The degree of precision and uniformity of the corner break has largely dictated the success and value of the manufacturing method.
Typically, these prior corner break forming assemblies have variously comprised grinding, milling, radial punching or press rolling of oil metering flat corners.
All of these methods have suffered from the fundamental problem of an inability to provide a substantially uniform and precise oil metering flat corner break. This problem is largely the result of the distinct forming of corner breaks at different times, with different forming pressures, by a variety of power sources, involving varying angular movement between the forming tool and the workpiece in a complicated milling, rolling or punching machine. Such complexities have made it virtually impossible to repeat identical forming conditions and, thereby, repeat the production of an identical corner break about the rotor. The problems of fixturing misalignment, power fluctuation, inconsistency in high pressure power tools running at a relatively high speed of operation, workpiece contamination and rapid wear of grinding wheels or milling tools have all contributed to the problems of the prior known methods and assemblies. In addition, where high tolerances have been demanded and have been sought to be maintained in the manufacture of such pieces, the manufacturing methods have been so slow as to produce a relatively expensive piece at an undesirable production rate.
The present invention contemplates a new and improved method and assembly which overcomes all of the above referred to problems and others to provide a new method of manufacture of a precision corner break on an oil metering flat for rotary valve, and an assembly for implementing the method which is simple in design, economical in manufacture of the work items, readily adaptable to a plurality of uses with workpieces having a variety of dimensional characteristics, easy to set up, easy to operate and readjust and which provides improved precision and substantially uniform corner breaks on an oil metering flat.